Field of the Invention
The present invention generally relates to musical instruments, and more particularly to hand actuated tremolo systems for use with acoustic guitars, with features that can also be used with electric guitars.
Discussion of the Background
Tremolo units are devices used to alter the pitch of a stringed musical instrument, such as a guitar, by changing the tension of the strings. Most embodiments of tremolo devices generally increase or decrease the tension of the strings when a lever, also known as a tremolo bar, moves a bridge that holds the strings in tension. In general, tremolo units have been exclusively designed for electric and semi-hollow body guitars. Though a useful and expressive tool for the electric guitarist, prior art tremolo devices designed for use with electric guitars are generally not compatible with acoustic guitars.
One type of tremolo has its roots in the Bigsby style of the 50's and 60's. The unit is fastened to the face of the guitar, and a large arm mounted on a tensioning spring governs an axle with six holes through which the strings pass. As the arm is depressed and the axle is turned, the tension and pitch of the strings is lowered. Variations on this format have recently been developed—some with axles that turn, others with tailpieces that slant forward. Some guitarists, however, find this style of tremolo too stiff for their liking.
The most common form for the tremolo is that found in the Stratocaster style of electric guitar. A large metal block through which the strings pass and terminate has a lever on top and springs on bottom. Six individual height (intonation) adjustment saddles are poised on top. The springs provide offset tension to counteract the pull of the strings. The steel bar sets into the block, and by rocking the bar, one can change the tension and the corresponding pitch of the strings.
Prior art tremolo devices, such as those described previously, however, are designed for electric guitars and are generally not compatible with acoustic guitars. Standard construction of prior art tremolo devices generally involves a bridge plate of a metal material that differs greatly from the porous, wooden material necessary to produce acceptable acoustic guitar tone. As can be appreciated, the sound produced by a standard acoustic guitar is significantly influenced by the manner in which the strings make contact with the fixed bridge of the guitar, as well as by the materials from which the fixed bridge is made. Prior art tremolo systems are not capable of transferring the vibration of the acoustic guitar strings through the bridge plate in a manner consistent with the production of acceptable guitar tone. Thus, the prior art metal device used with acoustic guitars would alter the sound of an acoustic guitar in an undesirable manner.
Moreover, the prior art method for attaching tremolo devices to an electric guitar makes them inappropriate for acoustic guitars. Threaded screws at least ½ inch in length go into the top surface of a solid body guitar as anchors for the standard tremolo device base plate. The string saddles are held against the top surface of the metal bridge plate by string tension and by a screw through each saddle. The screws, which are perpendicular to the top of the guitar body, must resist the full tension of the strings as well as remain upright against the rocking motion of the tremolo bridge when the device is in use. In a solid body guitar, enough wood surrounds the screws to allow mounting and use of the tremolo device without damage to the body of the instrument. Attaching a tremolo device to an acoustic guitar in the manner disclosed in the prior art with respect to electric guitar would place excessive stress on the top sound board. As referenced in Machinery's Handbook, 21st Edition, under “Permissible Working Stresses for Structural Timbers (U.S. Government Tests),” spruce (the type of material widely used for acoustic guitars) has the ability to withstand compression of 250 PSI perpendicular to the grain of the timber. With the thickness required for acoustic guitars, ⅛ inch or less, spruce, with this compression rating, is unable to support the screws necessary for mounting a tremolo device of an electric guitar without severe damage to the top sound board of an acoustic guitar. Further, the spruce top cannot resist the combined stress of 400 lbs. of tension placed against the mounting screws by the strings. It is unable to support the screws necessary for mounting such a tremolo device without severe damage to the top sound board of an acoustic guitar.
Another problem with tremolo devices, such as the Stratocaster style tremolo device, is an inability to return to the same tension and remain in tune after the tremolo device has been used. There are many factors in how a guitar returns to tune after use of a tremolo device. For instance, the strings must not grab in the nut slots or on the bridge saddles, or the breaking angle of the string over the nut must be correct. Guitarists may work around this retuning problem by using the tremolo lightly, using it only for the last song of a set, or adjusting the balance of the strings and the springs. Meanwhile, some manufacturers employ features such as rollers for saddles and nuts to minimize the chances that the strings will catch. In the last few years, a couple of locking mechanisms have been introduced on the tremolo. They all feature locking bridge saddles and locking nuts. However, such techniques require patient initial tuning to keep a guitar in tune during a lot of abuse.